For PVC foamed board, whether calcium carbonate filling affects the foaming performance is very complex, which mainly depends on the size, addition amount, dispersion and water content of calcium carbonate. If these factors of calcium carbonate are used properly, it can promote foaming, otherwise it will seriously affect foaming.

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There are two reasons why calcium carbonate can positively promote foaming: first, calcium carbonate can be used as nucleating agent to adsorb foaming gas to form bubble core, control the number of bubbles and make PVC bubbles finer; Second, calcium carbonate can improve the melt properties of PVC. Calcium carbonate with high rigidity can slow down the melt deformation and movement ability, so as to inhibit the rapid expansion of bubbles and control the finer size of bubbles.

Size of calcium carbonate: when the particle size of calcium carbonate matches with the foaming agent, it can play the role of nucleating agent and play a positive role in foaming. The specific suitable size is less than 5 μ m. Larger than non agglomerating dimension 1.5 μ m。 If the particle size of inorganic powder is greater than 10 μ m. Or it is too fine to cause self agglomeration and can not play the role of nucleating agent, which has a certain negative impact on foaming. I suggest 3000 mesh (4) μ m) Calcium carbonate, this size can ensure that the size is not greater than 5 μ m. It can also ensure that there is no reunion.

Calcium carbonate addition: appropriate calcium carbonate addition can promote foaming quality. Generally, it is recommended that the best filling amount is 10% - 20%. 

The addition of calcium carbonate is too low to form enough nucleation points in the melt, resulting in low foaming ratio; Too high addition of calcium carbonate can form many nucleation points, but too large filling and too low melt strength will lead to too much bubble breaking and also reduce the foaming ratio.

Calcium carbonate dispersion: if the inorganic powder is evenly dispersed in the resin, it can ensure that there is no agglomeration and that the size of calcium carbonate is 5 μ M size can be called nucleating agent, which does not affect foaming molding.The method to ensure the dispersion of calcium carbonate is calcium carbonate surface treatment. If the inorganic powder surface treatment is complete, the original hydrophilicity is completely changed to lipophilicity, and the foaming molding can not be affected. The specific surface treatment method can be parental treatment, that is, double treatment with aluminate coupling agent / polyol surfactant, or aluminate titanate coupling agent. One of the ways to ensure the dispersion of calcium carbonate is appropriate size, and the other is surface coupling agent coating. If the surface coating treatment of calcium carbonate is not complete, it will cause uneven dispersion, resulting in the agglomeration of fine powder into larger particles. Because the thermal conductivity of calcium carbonate is far greater than that of resin, it begins to absorb heat in the melt to form local hot spots, which reduces the strength of the melt near the hot spots. The foaming agent decomposes prematurely, resulting in the early foaming of the product before reaching the cooling area, resulting in no skin or poor skin on the surface of the product.

Water content of calcium carbonate: if the water content of inorganic powder is less than 0.5%, the filling basically does not affect the foaming molding.

Assist in stabilization: the pH value of light calcium carbonate is 9-10, while the pH value of heavy calcium carbonate is 8-9. Therefore, light calcium carbonate is more alkaline and can absorb a large amount of HCl produced by PVC decomposition. Auxiliary heat stabilizer plays a role in heat stabilization.

Particle size advantage: the particle size of light calcium carbonate is relatively fine, which can easily reach 2500 mesh. This kind of particle size is needed by PVC and can meet the performance needs of PVC pipes and profiles. The particle size of heavy calcium carbonate can only reach this size in the last 10 years, because the use habit is gradually choosing heavy calcium carbonate.

Eliminate color light: PVC products generally contain yellow color light, while light carbon calcium carbonate contains blue color light. Adding it can eliminate yellow color light.

Improving toughness: light calcium carbonate is beneficial to the impact strength modification of PVC products, while heavy calcium carbonate makes an outstanding contribution to the tensile strength.

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